Wind energy is one of the available forms of natural energy to be converted into electrical energy, and is more environmentally friendly compared with electrical energy coming from burning of fossil-fuel, such as petroleum or coal. The shape, outline and number of vanes of a wind turbine machine may affect the effectiveness of conversion from wind energy into electrical energy. A conventional vertical-axis wind turbine apparatus generally has elongated plate-like and nonperforated vanes. For vanes that can be propelled by wind blowing in a specific wind direction, a reverse wind flow may cause air resistance to hamper the movement of the vanes.
Referring to FIG. 1, a conventional horizontal-axis wind turbine apparatus is shown and includes an upright prop 31, an electrical generator 32 mounted on a top of the upright prop 31, and three vanes 33 coupled to the electrical generator 32. The vanes 33 are equiangularly spaced apart from one another about a horizontal axis (not shown). To enhance conversion efficiency, the vanes 33 are gerally made elongate. When wind in a direction (X) propels rotation of the vanes 33, a wind shear effect in a direction (Y) may be generated to cause noise. In order to reduce the wind shear effect and the noise, the vanes 33 are designed to have converged ends distal from the electrical generator 32 at the cost of reduced overall operation efficiency.